A methanol reformer system to produce power using a high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) for portable power generation applications is modeled. A detailed parametric study using computer simulations is conducted to estimate effects of the steam-to-carbon ratio (SC), the reformer temperature, the current density of the fuel cell, the fuel cell temperature, the cathode stoichiometric ratio, the hydrogen utilization, and the rate of power production on the reformate gas composition, fuel cell performance, input fuel flow rate, and the heat duties of the system components. We specifically examined the effects of the reformate gas composition at various fuel cell temperatures on the performance of HT-PEMFC. The results confirm that the CO molar ratio in the reformate gas increases with a low SC ratio and high reformer temperature. However, the effect of CO molar ratio on the fuel cell performance decreases at elevated fuel cell temperatures. The fuel cell voltage decreases similar to 78% with the variation of the current density from 0.1 A/cm(2) to 1 A/cm2 for 160 degrees C fuel cell temperature and 0.9% CO molar ratio in the reformate gas while it is similar to 61% for 180 degrees C fuel cell temperature. In addition, at elevated fuel cell temperatures from 160 degrees C to 180 degrees C, the input fuel flow rate to produce a given power generation from the system decreases, while enough heat is still available in the system to provide the heat requirement of different system components. (C) 2015 Elsevier Ltd. All rights reserved.